Development of Nanowire Optoelectronic Devices as Local Probes of Biomolecular Systems

Nanowire electrical injection laser., b, Shows an optical image of a functional laser device described in a, with emission from the end. c. Nanowire Avalanche Photodiode.

Recent advances in nanotechnology and biological sciences have opened exciting prospects for investigating direct interaction of electronics and optics with biological systems. These two broad areas of science share a number of similarities ranging from the similar length scales of building blocks and the common theme of bottom-up hierarchical assembly for producing functional systems. We will develop semiconductor nanowire-based optoelectronic devices to fabricate localized probes of biomolecular systems. Moreover, the small cross-section and very high aspect ratio of nanowires suggests their suitability to deliver extremely localized optical and electrical stimulus to biomolecular systems and also detect such signals locally. The primary hurdle to realize this goal is the development of highly efficient and active nanoscale light emitting systems such as LEDs and lasers and extremely sensitive nanoscale detectors possibly pushing the limits to single photon level detection. For this purpose we will grow and fabricate nanowire structures for highly efficient LEDs, lasers and detectors, and develop strategies for assembling nanowire devices at specific locations and in large arrays. Finally, we will explore the possibility of assembling laser-detector devices from single nanowires with extremely small gaps to enable “spectroscopy” on single proteins and biomolecular systems.

Biomechanical forces can regulate the development and maintenance of many human tissues. At the level of single cells, it is thought that externally applied forces can trigger traction forces generated by contractile machinery within cells, and that these forces together regulate numerous functions including proliferation, differentiation, gene expression, and cell death. To study this mechanically coupling between cells and their environment, we will develop a tool consisting of magnetic nanomaterials embedded into an array of elastomeric microposts that can apply forces to a cell through magnetic actuation of a few microposts and simultaneously measure traction forces generated at other microposts underneath the cell. The long-term objective for this study is to understand mechanotransduction, or how cells respond to mechanical stimuli. Significant advances in nanomaterial synthesis and biocompatible fabricated devices is necessary in order to develop the force actuator and sensor array (FASA).

Fluorescent Nanoclusters for Single Molecule Probes

Research in the Park group involves the synthesis and characterization of novel nanostructures and their applications in biophysical and medical research, such as their use as imaging tags for nucleic acids and proteins (Figure 1). Fluorescent metal clusters are of particular interest because of their small sizes and inherently diminished toxicity relative to semiconductor quantum dots. Currently, we are developing synthetic methods to prepare monodispersed and highly fluorescent gold clusters using a template based method. To improve the fluorescence quantum yield of the species, we will utilize an inorganic coating approach developed for semiconductor quantum dots. The main outcomes of this study will be 1) the generation of photostable fluorophores for single molecule optical spectroscopic studies, 2) the elucidation of the fundamental growth/etching processes important for the controlled synthesis of metal clusters, and 3) the development of detailed understanding on the fluorescence mechanism of these species. A reliable synthetic method that can generate water-soluble and fluorescent metal nanoclusters of varying dimensions will unlock the potential of metal quantum dots and provide a new architecture in which emission energy can be tuned over the visible and NIR spectral domains.

Piezoelectric NanoResonators for Biochemical Sensing

Gianluca Piazza,
Assistant Professor, Department of Electrical and Systems Engineering,
University of Pennsylvania

(a) Scanning Electron Micrograph (SEM) of a contour made AlN resonator; (b) mode of vibration and (c) corresponding electrical response. (d) Initial AFM analysis was conducted to study out of plane deflection in the resonator.

This research project focuses on the realization of piezoelectric nanoscale resonators for biochemical sensing. Chemically functionalized nanoresonators can be employed for the study of physical chemistry, DNA hybridization, biomolecular interactions and virus detection. Despite recent advancements in this area, the nanosystems developed to date still require bulky and ultra low noise optical or magnetic setups to detect resonant frequency shift, can hardly be operated in liquid environment and therefore do not permit real-time measurements. Dr. Piazza’s group is investigating the feasibility of fabricating nanoscale resonators that, for the first time, employ piezoelectric transduction mechanisms. Thanks to the large electromechanical coupling coefficient of a piezoelectric material such as aluminum nitride, the proposed nanoscale resonators can outperform existing technologies by providing real-time electrical detection of frequency shifts and maintain high quality factors also in liquid ambient by using bulk modes of vibrations.

A top-down nanofabrication approach for the reliable manufacturing of piezoelectric nanoresonators is under development. The nanoscale resonator is made out of a thin (0.5-2μm) AlN layer sandwiched between two metal electrodes. The width of the resonator sets its resonant frequency and can be varied between 100 nm and 500 nm. These dimensions are expected to produce devices with center frequencies ranging from 8 to 40 GHz. The high frequency of operation and the expected high Q of the nanodevice will provide high sensitivity to mass variations in the order of attograms and spatial resolution in the order of 50 nm.